The new Plastic ball or Poly ball will start to use in July 2014, a lot of forums and players has discussed about its effect and characteristic. But many people may not aware how ITTF test and approve a new ball, here is ITTF testing procedures and specification for references:
Picture source: modified from www.nittaku.com
ITTF Test Procedures
Picture source: modified from www.nittaku.com
The ITTF equilibrates balls at 230 Celsius, 50% R.H. for at least three days (standard conditions). They
are then tested as follows:
Weight is measured on an electronic analytical balance reading to 0.001g, and the results are rounded to
the nearest 0.01g.
Diameter We use a calibrated electrical device with an accuracy of at least 0.001mm which measures the diameter with a precision of 0.01mm.The ball is slightly pressed by a vertical pin (diameter 10mm). For fixation the ball is supported by an annular ring whose upper inside surface slopes at an angle of 45 degrees. The outer diameter of the ring is 40mm and the inner diameter at the bottom of this slope is 20mm. In this position the ball is placed between two lateral, horizontal flat measuring pins (diameter 6mm) which automatically adapt to the ball diameter by springs. The diameter of the ball is monitored while turning the ball with a mechanical device about the polar axis (1), an axis crossing the equator twice and comprising the center (2), and about further two arbitrary axes comprising the center of the ball (3,4).
By (1) the seam line is monitored, by (2) a line including both poles and by (3) and (4) arbitrary lines on the balls surface. By rotating the ball in said directions the minimum and maximum diameters are determined. The difference between the two values gives the lack of sphericity.
Alternatively, the following procedure can be applied:
The ball is placed arbitrarily between a flat and the measuring pin, and the diameter is observed. In order to guarantee that the measuring pin is vertically above the center of the ball we use two vertical flats with angle of 90o against which the ball is horizontally pressed during the measurement. By rotating the ball in various directions the minimum and maximum diameters can then be determined. The difference between the two gives the lack of sphericity.
Bounce is measured by releasing the ball mechanically. After its bounce on a standard steel plate the ball is monitored with a digital camera with a calibrated mm scale in the background. The photos are evaluated. The geometric mean of three determinations then permits calculation of the maximum height of bounce. Alternatively the rebound height can be measured by other methods, which give the same results.
Veer is a measure of the total sphericity of the ball, not merely its external aspect. It is measured by rolling the ball down a slight incline onto a horizontal surface, and measuring the distance by which it deviates from a straight line as it rolls across the surface. The incline is 100mm long at 14 degree to the horizontal; on a table that is 100cm long this gives a rolling time of about 3 seconds. Each ball is measured at least three times, rolling twice on the seam, and once about an arbitrary axis. A negative result is reported if the ball fails the test twice.
Hardness is measured on a fully automated and computerised Zwick tester (or equivalent). We use a preload of 0.5 N and testing starts 10 sec after preloading. A 20mm diameter pin presses against a pole of the ball with a 50 N force loaded at 10 mm/min, and the indentation is recorded with a precision of 0.01mm. The ball is supported by an annular ring whose upper inside surface slopes at an angle of 45 degrees. The outer diameter of the ring is 40mm and the inner diameter at the bottom of this slope is 20mm. Measurements are made on each pole and once on the seam; the average for the poles provides a measure of the hardness, and the difference between that and the seam indentation is a measure of the lack of symmetry.
Colour The ball colour is measured according to the CIE Lab system, giving three values L, a and b. L indicates the black/white value on a scale from 0 to 100; a indicates the green/red value; and b the blue/yellow value, both on a scale from minus to plus 100. The measurements are performed on the seam and two other points on the surface. 4 balls are selected from different boxes. The L, a and b values of the sample are determined by averaging over all 4 balls. "Dr. Lange Micro Color II" apparatus or equivalent is used.
Specifications
For the calculation of the following values two digits are taken into account.
B.1 Weight Conformity
Law 2.3.2 specifies 2.7g, but any weight between 2.67 and 2.77g is acceptable for any one ball. No more than 1 ball out of the 24 sampled may be outside this range. The sample mean must be between 2.69 and 2.76g. In carrying out statistical calculations we treat any weights less than 2.60g or greater than 2.85g as outliers.
B.2 Weight Regularity
The standard deviation may not exceed 0.03g.
B.3 Size Conformity
The minimum diameter of every ball must be at least 39.50mm, and its maximum diameter must not exceed 40.50mm. The sample mean average diameter, i.e. the mean of the average of the maximum and minimum diameters for each ball, must be in the range 39.60-40.40mm. Values below 39.25mm or above 40.75mm are considered in our calculations as outliers.
B.4 Size Regularity
The standard deviation of the average diameter may not exceed 0.06mm.
B.5 Sphericity Conformity
The sphericity of any ball must be less than 0.35mm, and the sample mean sphericity must be less than 0.25mm. (The sphericity of a ball - more correctly the lack of sphericity - is the absolute difference between its minimum and maximum diameters.) In our calculations values greater than 0.50mm are treated as outliers.
B.6 Sphericity Regularity
The standard deviation of sphericity must be less than 0.06mm.
B.7 Bounce Conformity
All 24 balls must rebound to a height of not less than 240mm or more than 260mm when dropped from a
height of 305mm on to a standard steel block.
B.8 Bounce Regularity (to be examined)
There is no specification for this property. Dynamic tests will be investigated.
B.9 Veer
No more than two balls shall deviate by more than 175mm from the center-line.
B.10 Hardness Conformity
The geometric mean pole hardness for any ball shall be in the range 0.71 – 0.84mm.
The geometric mean pole hardness for the sample shall be in the range 0.72 – 0.84mm
The mean seam hardness for the sample shall be in the range 0.75 – 0.85mm
The within-ball (uniformity) coefficient of variation of the measurements on each pole and once on the seam shall be no greater than 0.15mm.
The sample mean within-ball (uniformity) coefficient of variation shall be no greater than 0.06mm.
B.11 Hardness Regularity
The coefficient of variation shall be not greater than 0.06mm.
B.12 Colour
The specifications for the L, a and b values according to the CIE Lab system are
for white balls: a and b between -7 and +3
L exceeding 80
for orange balls: a between 10 and 35
b exceeding 40
L exceeding 70
All 4 balls tested have to meet these standards.
Articles above was from ITTF Technical Leaflet T3, June 2013.
